There have been attempts to improve fracture resistance and wear resistance of super hard alloy cutting tools and lengthen the life of tools by depositing a coating layer of titanium carbide, titanium nitride, titanium carbonitride, aluminum oxide, or the like on the surface of a WC-group sintered hard alloy or cermet substrate.
When cutting is carried out, particularly, when a workpiece which easily welds is cut by using these coated cutting tools, problems have frequently occurred in which the coating layer spalls away due to such welding and adhesion, and furthermore, fracturing of the substrate progresses, resulting in a decrease in the life of the tools.
In order to solve these problems, Japanese Patent Nos. 2105396 and 2825693 disclose a technique for suppressing welding and adhesion of a workpiece and enhancing wear resistance and toughness by improving surface roughness by mechanically grinding the surface of the coating layer at the blade-edge ridge of a cutting tool.
However, these techniques are insufficient to suppress the shortening of the tool life due to the progress of wear accompanying layer spalling at the rake face side and layer chipping at the flank side particularly in the case of cutting a workpiece of ductile cast iron, stainless steel, Inconel, or the like which easily welds and adheres.
Furthermore, since the surface roughness of a workpiece deteriorates, the desired roughness of the machined surface cannot be obtained in the case of finishing in which machining accuracy is required.
Recently, considering environmental problems, cutting without using a cutting oil (dry cutting) has become prevalent. However, in this case, due to loss of the lubricating effect of a cutting oil, welding and adhesion of a workpiece accelerates, and accordingly, decrease in the life and deterioration in roughness of machined surface have come into question.
Therefore, the main object of the invention is to provide a coated cutting tool in which fracture resistance and wear resistance are simultaneously realized, tool life is improved, and surface roughness of machined workpiece is improved.